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Science advice on the use of Timing Windows as a mitigation measure

National Advisory Meeting – National Capital Region

February 14–17, 2022
Virtual Meeting

Chairpersons: Mike Bradford and Karin Ponader


Fisheries and Oceans Canada’s (DFO) Fish and Fish Habitat Protection Program (FFHPP) has a regulatory regime in place to avoid, mitigate and offset the potentially harmful impacts of works, undertakings, or activities (WUAs) on fish and fish habitat. To manage these potentially harmful impacts, avoidance and/or mitigation measures such as timing windows are used to prevent or reduce the likelihood that a harmful impact will occur.

Timing windows are also called environmental windows or work windows, and are sometimes defined by their complement, e.g., restricted activity periods. They define lower-risk periods of the year during which the pressure imposed by a WUA may have a lesser effect on fish and fish habitat. Timing windows are a mitigation measure used by biologists and project proponents to reduce pressures that may have effects on fish, or may impair the habitat’s capacity to support one or more life processes of those fish. They are almost always used in combination with other mitigation or avoidance measures included in Letters of Advice or Fisheries Act Authorizations or other program instruments.

Timing windows currently in use are often developed by, or in collaboration with, provinces and territories, and vary by jurisdiction, species, or watercourse. The Projects Near Water website provides a list of tabs by territory and province (, with links to the respective provincial and territorial websites where instructions on how to identify specific timing windows can be found. Their description varies as they are developed by each jurisdiction based on their own approaches or templates. For example, in some cases, periods of the year when activity is to be restricted are identified (five provinces and two territories) while others define specific periods of when a WUA can take place (five provinces and one territory).

FFHPP is seeking science advice on the effectiveness of timing windows as a measure to mitigate pressures resulting from WUAs in freshwater, estuarine, and coastal environments. Advice generated by this process will assist FFHPP in the development of a science-based framework that could be used to guide the creation, modification, use, and assessment of timing windows. That framework may assist FFHPP to (a) rationalize the use of timing windows within FFHPP regulatory tools, (b) develop an approach for consistent and scientifically-defensible risk-based application of timing windows for FFHPP-regulated activities, (c) monitor and improve application of timing windows over time, (d) regularly update/amend timing windows to account for changes to the environment (e.g. climate change) or species status in collaboration with other jurisdictions as applicable, and (e) fill gaps and ensure a full nation-wide complement of timing windows.

It is expected that this process will also have synergies with other current Canadian Science Advisory Secretariat (CSAS) processes focused on habitat science advice, namely revisiting Pathways of Effects (PoE) diagrams in support of FFHPP risk assessment, estimating impacts and offsets for death of fish, and assessing cumulative effects in support of policy development and regulatory decision making. Information may also be used for application of provisions of the Species at Risk Act for cases where listed species may be exposed to the WUA. Science advice on the use of temporal avoidance to mitigate impacts of noise in the marine environment is found in other CSAS processesFootnote 1and will not be part of this process, although some of the principles may be applicable.


Participants will review Working Paper(s) and other information to address the following objectives:

  1. Review and synthesize examples of the use of timing windows to mitigate impacts to fish and fish habitat. This review will assist in the development of new timing windows, or the refinement of existing ones, and their application. The review may include, but is not limited to:
    1. Scientific studies that provide the ecological rationale for the use of timing windows, effectiveness studies, and frameworks or decision tools that contributed to the development of timing windows.
    2. Considerations and rationale used by other agencies (i.e., other governments and organizations) that may have contributed to the development, application, and evaluation of timing windows.
  2. Develop a standardized nationally-applicable set of criteria and/or scientific principles that should be considered in the development of a risk-based framework to guide the creation of effective timing windows, modification/refinement of existing timing windows, and their use.
  3. Provide advice on the design of studies to evaluate the effectiveness of timing windows. This may include research, monitoring, or modelling approaches.

Expected Publications

Expected Participation


Participation to CSAS peer review meetings is by invitation only.

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